Dealkylation of quaternary ammonium salts by thiolate anions: A model of the cobalamin-independent methionine synthase reaction.

Abstract

Dealkylation of quaternary ammonium salts by thiolate anions: A model of the cobalaminindependent methionine synthase reaction. Hilhorst, E.; Chen, T.B.R.A.; Iskander, A.S.; Pandit, U.K. Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Abstract: The reactions of thiolate ions derived from thiophenol and homocysteioe with substituted quatemary ammoniom salts result in alkyl tmnsfer from nitrogen to sulfur. A radical mechanism for this tmnsakylation, accounts for the reactivity pattern of the substrate salts. In a model study of the cobalamin-independent methionine synthase reaction, 5,5.6,7-tetramerhyl-5.6;7,8-tetrahydroptcridiniumsalt(25),whichcanbcconsidaedasamodelf~thenaMalUxxEymc 5-CH$-I4-folate (1). was allowed to react with the thiilate of homocysteiae, whereupon the won of m&ion& was observed in good yield. 'These results suggest that in the enzymatic prcnxss the N(S)-CH3 bond may be activated for the methyl transfer step, by uxndination of the N(5) with an electmphde or a proton at the active site.

Nucleophilic reactivities of tertiary alkylamines

“…Photolysis of the quaternary ammonium bromide 3e ‐Br − with Ar 1 =Ar 2 =Ph67 in CH 2 Cl 2 did not give rise to any absorbance of the benzhydryl cation (Ph 2 CH + ). This is not surprising because the Br − anion undergoes a diffusion‐controlled reaction with Ph 2 CH + ,48 and in CH 2 Cl 2 , the Br − anion would presumably form contact ion pairs with the ammonium ions, i.e., it can intercept the carbocation within the geminate solvent cage.…”

Amidine Dications as Superelectrophiles

“…In the MetE enzyme, where the transfer takes place directly to homocysteine, the currently accepted proposal 17 is that the N (5)-protonated ammonium salt 55 is the actual substrate for this transfer. Dicationic electrophiles have never been proposed as intermediates in that reaction, 18 but would a dication be a reasonable intermediate? It is known that tetrahydrofolates are easily oxidized structures, 19 and recent cyclic voltammetry studies on the closely related tetrahydrobiopterin 58 , 19 have shown a single two-electron wave in a reversible oxidation, implying that the second electron is transferred as easily or more easily than the first.…”

Identification of crinosterol from astigamatid mites

“…S-[Methyl-d 3 ]methionine was synthesized as described previously (Hilhorst et al, 1994). Homocysteine (500 mg) and 1,8-diazabicyclo[5,4,0]-7-undecene (2 ml) were dissolved into acetonitrile (50 ml).…”